Back when I was new at the freight hauling game (ie, about three months ago)I loaded a C402 up to the gills and started doing a weight and balance calculation. My PIC looked at it and said "No way that's eighty pounds" (or whatever the number was on the manifest). We called the loaders over and figured that addition was perhaps beyond their range of skills.
Made me realise that not trusting the paperwork was important though.